Stop group of Seals holding back resentment (6)
I believe the answer is:
period
'stop' is the definition.
('period' can be a synonym of 'stop')
'group of seals holding back resentment' is the wordplay.
'group of seals' becomes 'pod' (I can't justify this - if you can you should give a lot more credence to this answer).
'holding' means one lot of letters goes inside another.
'back' says the letters should be written in reverse.
'resentment' becomes 'ire' (I've seen this before).
'ire' back-to-front is 'eri'.
'pod' placed around 'eri' is 'PERIOD'.
Can you help me to learn more?
(Other definitions for period that I've seen before include "Indefinite length of time" , "Era, epoch" , "Duration or interval" , "Amount of time - US full stop" , "term" .)